In making a laminate, a fibrous substrate is impregnated with a resin which is then partially cured to form a prepreg, and a stack of prepregs is heated under pressure to form the laminate. The properties of the laminate depend to a significant degree on the characteristics of the interface between the substrate and the resinous matrix. In particular, the strength of the laminate is usually a function of the adhesion between the fibrous substrate and the resinous matrix. Many efforts have been made to alter the surface characteristics of fibrous substrates to increase the desirable properties of laminates. These include physical or chemical treatment of the fibrous material itself, as well as coating the fibrous material with another material which is more compatible with the resinous matrix. Many difficulties have been encountered using these techniques, depending on the particular technique, but one problem that has not been overcome is how to bond a compound to the fibrous substrate when the compound and substrate do not have a polymerizable structure and therefore are not polymerizable. Such compounds include the saturated aliphatic hydrocarbons such as pentane, hexane, and dodecane.
Another problem arises when the laminates are made from a polyaramide fibrous substrate in an epoxy resinous matrix for use as a printed circuit board. These circuit boards are used for very high speed circuit carriers (VHSIC) and have leadless chip carriers soldered directly onto the circuit board. While the thermal expansion of the polyaramide fabric-epoxy circuit board matches that of the solder fairly closely, on thermal cycling microcracks tend to appear in the circuit board which can break the circuit, resulting in a failure of the equipment. It is not known whether these microcracks begin at the interface of the polyaramide fibers and the resinous matrix or begin within the resinous matrix itself.